[ghc-steering-committee] [Proposal] #193: Make `forall` a keyword in type (recommendation: accept)

[Simon Peyton Jones]

I'm supportive.

Simon

| -----Original Message-----
| From: ghc-steering-committee <ghc-steering-committee-bounces at haskell.org>
| On Behalf Of Eric Seidel
| Sent: 06 February 2019 00:51
| To: ghc-steering-committee at haskell.org
| Subject: [ghc-steering-committee] [Proposal] #193: Make `forall` a keyword
| in type (recommendation: accept)
| 
| This proposal suggests making `forall` a keyword at the type-level.
| `forall` is currently only a keyword when `-XExplicitForAll` is enabled.
| 
| This change would avoid a potentially confusing situation where the meaning
| of a type can change based on which extensions are enabled. For example,
| 
| ```
| f2 :: forall a -> a -> a
| ```
| 
| with no extensions, the `forall a` would be interpreted as two regular type
| variables. But if we enable the upcoming "visible dependent quantification"
| extension (I assume there's an extension involved here somewhere, the
| proposal doesn't say), the `forall a` would be interpreted as a *single*
| dependently quantified type variable `a`.
| 
| The only concerns are that this change could break existing programs, and
| that it moves us further away from the standard. I'd be very suspicious of
| any programs that used `forall` as a type variable, as that's just ripe for
| confusion. And it's a very small step away from the standard, so I don't
| think that should stand in the proposal's way either.
| 
| I recommend we accept the proposal.
| 
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